Nuclear fusion is the process by which two or more atomic nuclei join together, or “fuse”, to form a single heavier nucleus. This is usually accompanied by the release or absorption of large quantities of energy.
The fusion of two nuclei with lower masses than iron generally releases energy. In theory it is possible to build nuclear reactors that deliver ten times more fusion energy then is required to cause the fusion reaction. However these large-scale thermonuclear fusion processes, involving many nuclei fusing at once, must occur in matter of very high densities and temperatures. One way to achieve controlled fusion is to apply a rapid pulse of energy to the surface of a microcapsule or pellet of fusion fuel, causing it to “implode” and heat to very high pressure and temperature. If the fuel is dense enough and hot enough, the fusion reaction rate will be high enough to burn a significant fraction of the fuel before it has dissipated. To achieve these extreme conditions, the initially cold fuel must be explosively compressed.
Laser inertial confinement is a fusion technique that uses a laser as an energy source to implode a microcapsule filled with fuel. One type of microcapsule used in this application is a hollow shell of beryllium doped with copper and filled with gas of deuterium (D) at a pressure of nominally 20 atmospheres. These beryllium shells are nominally 2 mm in diameter with shell walls nominally 100 μm thick.
Copper doped beryllium hollow shells are made by sputter deposition of beryllium with a radially graded copper dopant onto plastic mandrels. Shell walls have been reported between 20 μm to 100 μm thick. A small hole of nominally 6 μm or less in diameter is laser drilled into the shell wall. The hole is used as an escape hatch to remove the organics of the mandrel during pyrolization. By forcing hot air at about 450° C. into and out of the shell, the plastic mandrel is pyrolized with outgassing through the 6 μm hole. The 6 μm hole is also used as the opening to fill the shells with the deuterium gas. After filling, the hole is sealed by positioning the shell on an XYZ stage where UV glue is applied using two microscopic cameras and a metal tube.
There are a number of challenges associated with this process. Laser drilling the hole requires precision so as not to cut through to the other side of the shell. Pyrolization is challenging because it is difficult to get air in and out of the small opening. Because the hole is quite small, gas flow through the orifice must be forced with an external pressure variation. Further calculations showed that because the volume of the capsule is quite small and the amount of plastic in the shell by comparison is large, the “pumping” of air in and out of the shell must occur at least once per minute in order to supply enough O2 to completely burn the plastic to CO2 and H2O in a reasonable time. After removal of the mandrel, the shell is pressurized and sealed at about 20 atmospheres with 99.6% D. This is done by placing the shell in a pressurized chamber on an XYZ stage viewed with two microscope cameras As shown in the FIG. 5 prior art process, the shell is positioned using the cameras and stage and UV glue is applied with a metal tube attached to a modified valve in the top of the shell. This process requires “hand crafting” of each shell and cannot be economically scaled to production quantity needed to sustain a nuclear fusion reactor.